Repairs Ariens EZR 1542 won't start after electrical short.....

The Diode will probably solve some problems, but I still believe (somehow) this is connected to the original "short" that made the throttle cable hot and melt the cover.
If it truly was a short, there must have been a wire somewhere that came in contact with the throttle cable. Is that part of the cable anywhere near the exhaust ? If this is a normal throttle cable there is a metal push/pull wire that is inside a spring conduit (should be constant continuity from wire to spring) I can't figure out how it could get hot in only one spot unless there is not normally full continuity and positive touched ground somewhere in that cable. ????? :confused2: I might (at this point) take the throttle cable completely off and inspect it from one end to the other.
Something is shorting somewhere that blows that fuse !

Well, at this point, I have replaced the diode plug with a brand new one, and once again it will not turn over or crank at the ignition switch AT ALL. Still turns over good and strong all day with metal touched to the contacts on the starter solenoid, but not putting any fire to the switch or starting in any way. So at this point, I am completely and totally lost and have no idea where or what to even check next...Ugh...I can't help but think it is something fairly simple, but I hate having no idea what it possibly could be or where to even look next in the troubleshooting process to try and fnind out..... :confused2:

I'm guessing that you have disconnected the battery and checked the continuity of each of the wires that is involved in the circuits to key switch and starter.

Have you also checked continuity to ground for each of those wires that should not go to ground ? There may be one of those wires that shows continuity to it's intended contacts, but also is grounding out somewhere.

SOMETHING caused a short that made that throttle cable hot. :confused2:
SOMETHING is not allowing the circuit to connect normally to the starter. :confused2:

I wish I could see the machine myself -- at this point, I might just start replacing wires with new ones and new switches etc.

You deserve credit for not giving up ! :thumbsup:

GOOD LUCK !